In general, there are two types of projector apparatuses: a system using a liquid crystal panel and a system using a DLP. In addition, in the system using a liquid crystal panel, there are one-sheet types and three-sheet types. In either system, radiation light from a light source is divided into three colors (RGB). In a liquid crystal panel transmission of light is adjusted according to image information in a liquid crystal panel, and the three colors which pass through the panel are synthesized so as to be projected on a screen. In the system using a DLP, there are also one-sheet types and three-sheet types. In the case of the one-sheet type, radiation light from a light source is irradiated in a time dividing manner, to a space modulation element (which is also referred to as a light modulation device, specifically, referred to as a DMD element etc.) through a rotation filter where RGB areas, which are separated from one another, are formed. This allows the DMD element to reflect the selected light irradating the screen. In such a DMD element, millions of small mirrors are arranged side by side, wherein projection of light is controlled by controlling direction of each small mirror.
A high pressure discharge lamp with a high mercury vapor pressure is used as a light source of a projector apparatus. This is because a high output of light in visible wavelength band is obtained by having a high mercury vapor pressure. Moreover, in this kind of discharge lamp, a projection(s) is formed at the tip of an electrode(s) during lighting. For example, in Japanese Patent Application Publication No. 2002-175890, existence of such a projection(s) is viewed as a problem. Further, '890 introduces technology that removes this projection, specifically, '890 inserts a low frequency (for example, 5 Hz) for 1 second or more in a stationary frequency, to completely eliminate the projection on an electrode surface.